Carl von Clausewitz, the imposing German general whose theories about war remain influential nearly 200 years after his death, observed that "public opinion is won through great victories and the occupation of the enemy's capital." Not anymore. For one thing, it's hard to determine what "great victories" look like these days. We may have gotten rid of Osama Bin Laden in 2011, but three years later, Jeh Johnson, the secretary of homeland security, is telling us that the profusion of jihadi fighters in Syria means that "Syria has become a matter of homeland security." In other words, what happens in the killing fields of the Middle East has consequences at home.

Meanwhile, military planners, with one eye on the experiences of Afghanistan and Iraq, are increasingly wary of the political costs of putting boots on the ground. After 9/11, military spending surged from 3.5 percent of GDP in 2001 to 5.7 percent in 2011. Many Americans now believe that it's time to rein in such profligacy and to spend our money on domestic concerns. The palpable sense of "war fatigue" stretches all the way from the left of the Democratic Party to the Senator Rand Paul wing of the GOP.

But while Americans may have tired of foreign wars—particularly wars without defined endings—foreign wars haven't tired of us. That's why we should continue debating what our defensive posture should be and how much we should spend to maintain it. But instead of having that debate, we have sequestration—the process in which progressively deeper forced cuts are apportioned roughly equally between defense spending and discretionary domestic spending—resulting in a completely pointless public blame game over whose fault it will be if those cuts take place.

Derived from the Latin verb "to withdraw," sequestration conjures up unfortunate associations with a declining Roman Empire. The American version, of course, stems from the 2011 Budget Control Act and was meant to force us to get control of the budget. As far as Defense Secretary Chuck Hagel is concerned, though, sequestration itself is among the most tangible national security threats we face. As he told the House Appropriations Committee in March, further sequestration in fiscal year 2016 will endanger "America's traditional role as a guarantor of global security, and ultimately our own security."

Hagel is far from alone in loathing sequestration, which has all the subtlety of a Russian tank crossing an international border. In August last year, President Barack Obama pledged, before an audience of U.S. Marines, to continue "working to get rid of the sequester," which, like Hagel, he dismisses as "something that Congress has proposed." (For what it's worth, the Washington Post's Bob Woodward disputes Obama's account, claiming that the president approved the scheme after it was cooked up by his advisers.)

But the squabbling over sequestration has obscured a more important discussion—the Obama administration's defense strategy in a world that, as Senator John McCain asserted during a Senate budget hearing in March, "is more unsettled than any time since the end of World War II."

At that same hearing, McCain lambasted Hagel's reduced defense budget, even as he acknowledged that the defense secretary's room for maneuvering was limited. McCain was particularly irked by Hagel's plan to reduce the size of the army to 440,000-450,000 soldiers, the lowest number since before World War II, especially as that announcement coincided with Russia's invasion of Ukraine and its seizure of Crimea. "Your timing is exquisite," he told Hagel.

What rightly worries defense hawks is the Obama administration's apparent jettisoning of a strategic concept that has been in place since the defeat of the Axis in 1945. Known as the "two war force sizing construct," its purpose is to enable us to conduct two major wars simultaneously. While the concept has a historical pedigree—at the height of the British Empire, the Royal Navy's fleet was deliberately designed to overcome the capabilities of its two nearest rivals—it also involves a leap of the imagination, in that it sets an ideal operating level for U.S. forces. Being able to win convincingly on two fronts, the logic goes, deters our enemies from starting conflicts in the first place.

Supporters of the administration say the two-front concept hasn't been junked, merely revised. According to the Strategic Guidance document issued by the White House in early 2012, the new thinking concentrates on winning on one front while "imposing unacceptable costs" on the aggressor on a second front. To many defense analysts, however, that's just wordplay; what matters in the end is not only how we project our strength, but how others perceive that projection. And increasingly, those others—our adversaries in Moscow, Tehran, Pyongyang and other rogue capitals—plainly regard America as being in retreat.

For example, we announced that we were halving the number of U.S. Army brigades in Europe in 2012—a fact that Russian President Vladimir Putin likely took into account when he decided to invade Ukraine. In Afghanistan, where Al Qaeda was incubated, our troop presence looks set to drop to below 5,000, even though General Joe Dunford, who leads NATO and U.S. forces in the country, has made clear we need at least 10,000 soldiers to effectively train and assist Afghan forces fighting the Taliban-led insurgency. In Syria, we have famously dithered in confronting the brutal Assad regime, indirectly allowing jihadi units to fill the vacuum. Signals like these are read only one way in countries like North Korea and Iran: Pulling back is an admission of loss, and your loss is our gain.

None of this means that the current administration is deliberately compromising our defenses. But it does mean that the decisions we make now, and the way our enemies interpret them, will define the global power balance for decades to come. The great Irish diplomat and scholar Conor Cruise O'Brien once opined that problems have solutions, but conflicts have only outcomes. However hard it may be to hear, it is on that piece of wisdom, and not on the twists and turns of public opinion, that a viable defense strategy—and therefore an appropriate Pentagon budget—rests.